Wheelchairs for use by handicapped and disabled persons have been well known for many years. These wheelchairs fall into two basic categories, manual wheelchairs and power wheelchairs. Power wheelchairs use a motor system for driving one set of wheels on the chair. Depending on the location of the set of wheels that are driven, the wheelchair is categorized as either a front, mid or rear wheel drive wheelchair. Each type of chair has its advantages, disadvantages and design complexities.
In a rear wheel drive wheelchair, the wheelchair includes powered wheels that have an axis typically behind the center of gravity of the wheelchair and occupant. In this chair, there are generally two caster wheels that contact the ground located at or near the front of the chair. These front casters provide support and balance for the wheelchair. Rear wheel drive power wheelchairs also typically have small anti-tip wheels on rigid mountings to the rear which are designed to catch the wheelchair if it should start to tip backwards.
One example of a rear wheel drive power wheelchair is shown in U.S. Pat. No. 5,540,297 to Meier. This wheelchair has the large powered wheels mounted on sprung trailing arms, and has the rear anti-tip wheels mounted on the ends of the trailing arms.
Power wheelchairs are also known in which the drive wheels are positioned forward of the center of gravity, and the wheelchair normally rests on the drive wheels and on rear caster wheels. These include wheelchairs, known as mid-wheel drive power wheelchairs, in which the drive wheels are aligned close to the position of the center of gravity. In this type of wheelchair, anti-tip wheels are provided at the front to support the wheelchair if it should tip forwards and to assist it in climbing curbs and ramps. Commonly-assigned U.S. Pat. No. 6,129,165 shows a mid-wheel drive power wheelchair in which the front anti-tip wheels are inter-linked to the drive wheel suspension.
One of the deficiencies with conventional rear wheel drive power wheelchairs has been that the anti-tips wheels that are located on the rear of the frame are typically fixed mounted such that there is no vertical change in position. This type of arrangement can pose a problem when accelerating on an incline.
Also, in rear wheel drive power wheelchairs, because of the location of the drive wheels aft of the center of gravity, the wheel base tends to be fairly long, thus increasing the turning radius of the wheelchair.
A need, therefore, exists for an improved rear wheel drive power wheelchair.